Contemporary science issues Lesson 14: Has the universe always been there? © 2006 Gatsby Technical Education Projects

Has The Universe Always Been Here? The Evolution of the Universe.

Learning Outcomes All students are able to recall the main ideas for the evolution of the Universe. Most are able to match the key ideas of the evolution of the Universe to the main sources of evidence. Some can explain red shift and how it provides evidence for an expanding Universe.

The Milky Way The Moon The Solar System The Earth The Universe How big is the Universe? Sort out the following in order of their size (smallest to largest): The Milky Way The Moon The Solar System The Earth The Universe

The Solar System ~ 12 Billion km How big is the Universe? Sort out the following in order of their size (smallest to largest): The Moon ~ 3500 km The Earth ~ 12500 km The Solar System ~ 12 Billion km The Milky Way ~ 100 000 Light Years The Universe ~ 50 Billion Light Years

What is a Light Year? A “light year” is the distance travelled by a ray of light in one year. If light travels 300 000 km every second, how far would it travel in one year? Number of seconds in one year = 60 x 60 x 24 x 365.25 = 31 557 600 Distance light travels in one year = 31 557 600 x 300 000 ~ 9 500 000 000 000 km A car that travels at 100 km/h (about 60 mph) would take nearly 11 million years to travel that distance.

How big is the Universe? The visible universe is huge! The question that has been puzzling people for thousands of years is: Where does the universe come from? How and why do we “make a theory” and what do we need to support our theory?

Where did the Universe come from? Many different theories have been put forward to describe how the universe began or to explain why it is here. The earliest accepted theory was proposed by the Greeks.

A Timeline of Theories 2500 2000 150 100 50 Number of years ago (~2500 years ago) Static Universe: The Universe does not change with time. It appears the same every time it is observed. When were the theories first suggested? What do you notice about the amount of time between the theories? (~80 years ago) The Big Crunch: The Universe expands to a certain size before gravity causes it to collapse in on itself. (~50 years ago) The Big Bang: The Universe began with all matter concentrated in a small volume that suddenly expanded. Number of years ago 2500 2000 150 100 50 (~2500 years ago) Infinite Universe: The Universe has no edge. It carries on forever in all directions. (~80 years ago) Slowing Expansion: The Universe expands forever but the expansion becomes slower. (~80 years ago) Accelerating Expansion: The Universe expands forever but the acceleration becomes faster. (~50 years ago) Steady State Universe: The Universe has no beginning but it does expand. The gaps that form are filled in with new matter.

Task 1 Look at the cards that describe the theories of the evolution of the universe. Divide the theories into two groups (e.g. Those with a with a beginning and those without) How else could you group the theories?

What do we think now? Even today scientists are not agreed on what will happen to the universe, though they do have some idea. Scientists have made observations that they use to develop and support their theories. We are now going to look at these observations.

The Unchanging Universe When you look into the sky at night the stars are in the same positions as they were the night before. In fact their positions have changed very little since the time of the Ancient Greeks. So, why do you think the Ancient Greeks thought the universe was unchanging? How long would you need to observe the stars to see changes happen?

The Gravity Riddle The Greeks and religions thought the universe was static, its size was constant. Is this possible? Gravity would cause the universe to collapse in on itself! Do we see this happening? The only solution to this was for the galaxies to be moving away from each other. The universe was expanding! But where is it expanding from?

Red Shift In 1929 Hubble showed that the wavelength of light from stars had been “stretched” or red-shifted. This was evidence that the stars and galaxies in the universe were moving away from each other. The universe was expanding. Hubble also discovered that the further away from us a galaxy was the faster they were moving! What does this mean?

Cosmic Microwave Background If the universe began with a “Big Bang” scientists expected there to be a small amount of heat energy left over. This left over energy has been detected and is called the Cosmic Microwave Background. The Cosmic Microwave Background means that space has a temperature 3 °C above absolute zero.

Task 2 Using the cards, match the evidence to the theories they support. (Some cards might go to more than one theory) Why do you think the Ancient Greeks thought the Universe was “Static” or unchanging? Which theory do you think is most likely? Which of Friedmann’s Universes do you think is right? Why?

Why did people living in Ancient times draw the conclusions they did? What is the need for scientists to observe the universe over longer period of time? What is the need for evidence?

Extension Why is the sky dark at night? The answer to this question might seem obvious; That the night side of the Earth is facing away from the Sun. In fact the answer is not so straightforward.

Olber’s Paradox Our Sun is one of a seemingly infinite number of stars in our infinitely large Universe, each one emitting light. If the number of stars is infinite then each patch of the sky would be covered by a star. Every line of sight would end on the surface of a star (see picture). No matter how far away these stars are from Earth some of their light would reach us. Therefore light would be coming from all parts of the sky. Even at night! This means that the night sky should be at least as bright as the sky in the day! From everyday experiences we know this is not the case. (look at the sky at night!)

The Answer? If an infinite universe would be very hot and bright why is our universe cold and dark? Perhaps its not infinite!! This means that the universe could have a beginning!